Adhesives and sealants are widely employed in many industrial manufacturing processes. Adhesives are employed to bind various substrates together. Sealants are employed to produce load bearing elastic joints between two or more surfaces and to prevent the passage of air, water and dirt through the joints. The automotive industry, in particular, is a major user of adhesives and sealants. Automobiles are assembled from several structural components which are joined together in various fashions depending on the particular components and the degree of stress that will have to be endured. For certain assembly steps an adhesive composition is applied as a liquid and subsequently hardened to provide sufficient bonding strength. For example, adhesives are utilized in the assemblies of door panels, quarter panels, tailgates and roofs. These same assemblies also employ sealant compositions at a later stage in the assembly line. Still other automobile assemblies which are welded or bolted together use sealant compositions in their seams. The wheel house, shock tower, rocker panel, firewall, floor hem flange, floorpan, and trunk are a few examples of where sealants are employed.
Automotive adhesives and sealants are typically made of plastisols, i.e., dispersions of polymeric resins in plasticizers. Typical polymeric resins include poly (vinyl chloride), poly (vinyl acetate) and copolymers of vinyl chloride and vinyl acetate. Other polymers can be employed as well in the preparation of plastisols. Plasticizers are high boiling liquids which attack and plasticize the polymeric resin particles. Plastisols are liquids which are applied at room temperature to fill seams and body joints which need to be sealed. The liquid is converted to a solid through exposure to heat. In effect, the heat causes the dispersed resin particles to fuse together. A solid product results upon subsequent cooling. Plastisols can be painted over without leaching or causing other cosmetic problems. Finally, they are durable enough to withstand normal weather and user exposure. Another important quality of plastisols is that they are not expensive.
Since the adhesion of a plastisol to cold-rolled-steel or electrodeposition coatings (E-coat) is poor, conventional adhesives and sealants must contain adhesion promoters. Known adhesion promoters for adhesives and sealants include polyamidoamines, polyamines, epoxy resins, reaction products of polyamines and epoxy resins, blocked isocyanates, organofunctional silanes, mixtures of urotropine and resorcinol, and combinations thereof. The adhesion promoter typically represents from about 3 to about 15 weight percent of the entire adhesive or sealant composition. Various adhesion promoter systems are described in U.S. Pat. Nos. 4,146,520, 4,151,317, 4,268,548, 4,440,900, 4,533,524, 4,540,731 and 4,673,710.
In the manufacture of automobiles and other articles of manufacture, the bodies and frame assemblies thereof are coated, or primed, electrostatically with a 100 percent solids powder spray. The compositions of such powder sprays, referred to in the automotive industry as "powder prime", and methods of electrostatically applying the powder prime are well known to those skilled in the automotive industry. It is estimated that on the order of 25,000 pounds per month of 100 percent solids waste powder prime may be generated at each assembly plant in which it is used to prime auto parts, such as frame assemblies. That powder prime which does not remain affixed to the primed auto part and which is recovered subsequent to the electrostatic deposition of the powder prime thereon, is transported as waste to landfills for disposal.
U.S. Pat. No. 5,710,199 discloses an additive for automotive sealants which is composed of a dispersion of waste powder prime in a plasticizer. The waste powder primes disclosed in U.S. Pat. No. 5,710,199 are generated from conventional electrostatic deposition processes. Typically, these primes contain a polymeric resin, such as a polyester, a polyester/acrylic copolymer or a polyester/acrylic/polyurethane terpolymer. The plasticizer can include, e.g., 2-ethylhexyl diphenyl phosphate, diisoheptyl phthalate, a linear phthalate based on C.sub.7 -C.sub.9 alcohols, and a mixture of esters and dipropylene glycol dibenzoate. The resulting additive is blended with a polymeric film-former such as poly(vinyl chloride), poly (vinyl acetate) or copolymers of vinyl chloride and vinyl acetate to form the automotive sealant product. The automotive sealants described in U.S. Pat. No. 5,710,199 do not require adhesion promoters in order to bond to primed surfaces and E-coat.